There are many mechanical constructions which benefit from the delivery of lubricating fluid to an interior of a rotating shaft. One such construction is found in gas turbine engines where drive splines between an internally splined drive shaft and an externally splined driven shaft are lubricated by a supply of lubricant fluids trapped in an annular reservoir within the drive shaft. In order to ensure a sufficient supply of lubricant fluid in the annular reservoir, it is desirable to deliver lubricant fluid to the reservoir from a source. However, the centrifugal forces generated by the rotation of the shaft tends to eject lubricant fluid from the hollow shaft, so lubrication is difficult to achieve using conventional methods of lubrication such as immersion in lubricant fluid. Consequently, a pressurized delivery system is required.
Systems for delivering a pressurized lubricant fluid into a rotating hollow shaft, are known. For example, U.S. Pat. No. 5,119,905, which issued on Jun. 9, 1992 to Murray, describes an accessory drive spline lubrication system for a turbine engine reduction gear box. In this system, one or more nozzles spray a stream of engine oil directed at an angle towards the axis of the drive shaft and towards orifices in the drive shaft. The nozzles are stationary relative to the drive shaft. Each nozzle directs a stream of lubricant toward an annular reservoir located near the splines, the streams being aimed at the orifices. The streams of lubricant, however, are intermittently interrupted by the rotation of the drive shaft.
As a further example, U.S. Pat. No. 5,246,087, which issued on Sep. 21, 1993 to Schippen, discloses a device for radially transporting a medium to a rotating station. The device includes a bearing assembly having a stationary outer cylinder with a lubricant feed, an inner cylinder which is rotatable together with a receiving station that is coupled via rotation bearings to the outer cylinder. The two sealing rings seal opposite ends of the housing and form a passage for lubricant fluid medium. The patent emphasizes that, in all conditions, the medium for transfer (lubricating fluid) cannot leak into the environment. This device is therefore unsuitable for use in high temperature operating environments such as encountered in turbine engines because the leak-proof seals would likely fail under such conditions.
Yet another example is disclosed in U.S. Pat. No. 4,251,186 which issued on Feb. 17, 1981, to Chomel et al. This patent discloses a device for circulating fluid in a hollow shaft. The device includes a fixed stator coaxial with the hollow shaft which passes through it, forming an annular chamber around the hollow shaft and a rotor within the chamber. The rotor includes a plurality of radial bores. When the shaft is rotated, a centrifugal force acts on the oil in the radial bores to drive the oil into the chamber and to draw oil through a port around the shaft in the stator. The pressure established in the chamber overcomes the centrifugal force generated by rotation of the shaft and drives the oil in the chamber through radial bores into an interior of the hollow shaft. An annular separating wall around the shaft within the chamber is fixed to the chamber and defines, together with a sidewall of the stator, an annular intake chamber which directs the pressurized oil into the radial hole of the shaft.
A drive shaft of a gas turbine engine typically operates at rotational speeds of up to about 6000 RPM and at temperatures of up to about 200 degrees F. As a result, to be delivered to the interior of the hollow shaft lubricant fluid must be under pressure.
A lubricant system used for the power shafts and accessory drive shafts of gas turbine engines is located within a housing in which the shafts are rotatably mounted and a certain amount of leakage is permitted. However, leakage reduces the pressure at which the lubricant fluid is delivered and seals having too much clearance are not acceptable for applications such as the high speed, high temperature and high lubricant fluid pressures associated with gas turbine engines.